The present invention relates to the field of orthopedic splinting/casting materials and packaging for the same. More particularly, the present invention relates to curable orthopedic splinting/casting material in a heat sealed hermetic package which includes means for facilitating tearing of the package in a predetermined direction.
Hermetic packaging constructed from heat sealable laminated materials is well-known. Many products are placed in such packages to extend their shelf life by sealing the products from exposure to air, water vapor, etc. Heat sealed hermetic packaging constructed from laminated sheet materials is especially popular because of its relatively low cost as compared to effectiveness.
The hermeticity of such packages is especially important in the field of packaging for curable orthopedic splinting/casting materials. Such products are discussed in U.S. Pat. Nos. 4,433,680; 4,609,578; 4,667,661; 4,774,937; and 5,027,803, all of which are hereby incorporated for their disclosures relating to those materials. Briefly, however, such products are extremely sensitive to ambient levels of water vapor and will harden (i.e., "cure") upon exposure to very low levels of water vapor. Once hardened, the product can no longer be used for its intended purpose and must be discarded. Because of their sensitivity, such products are typically packaged in single-use hermetic packages as constructed from composite laminate sheet materials.
Hermetically sealed packages constructed from laminated sheet materials are, however, typically difficult to open due to the nature of the materials used to manufacture them. The laminated sheet materials typically comprise three or more layers chosen for their strength, moisture impermeability, and/or heat sealability. The composite material is difficult to tear and is particularly difficulty to tear in a desired direction. As a result, users must typically first tear the package once and additionally tear, cut or, for example, open one of the heat sealed ends to provide a large enough opening to allow adequate access to the product inside.
One attempt to provide heat sealed hermetic packages which provide predictable tearing characteristics is discussed in U.S. Pat. No. 4,598,826. Tear strips are laminated to the interior of the package to facilitate tearing of the package in a desired direction lying along the tear strips. Such packages are, however, difficult to manufacture as the tear strips must typically be introduced as the package is formed from the laminated sheet material. In addition, the hermeticity of the packages can be compromised if the tear strips are included in the heat seals because of their relatively large profile which is difficult to accommodate in the heat seals without forming leaks.
Another attempt at addressing the difficulties in opening such packages includes forming heat sealed packages with lines of weakness across one of the heat seals as described in U.S. Pat. No. 4,139,643. The lines of weakness are provided to enhance the predictability of opening the packages. One disadvantage of this approach is that the package can only be predictably opened along the heat seals. In many instances that opening is not large enough to provide sufficient access to the product without further tearing or cutting to enlarge the opening in the package.
Another disadvantage of providing lines of weakness is the opportunity that they present for leaks into the package. Such features may be particularly vulnerable to flex cracking which can break the thin foil vapor barrier layer used in the laminate sheet materials.
Yet another approach to providing predictable opening characteristics for heat sealed hermetic packages is described in U.S. Pat. No. 4,279,344. The packages discussed in that reference include a heat sealable inner layer, metal foil vapor barrier layer and outer layer to protect the metal foil. The heat sealable inner layers form a peelable bond which is easily separated by the user. One disadvantage to this approach is that the bond formed is designed to be weak enough to allow for easy separation which can lead to failure of the package to maintain its hermeticity during shipping and handling.
European Patent Publication No. EP 0 471 220 discloses an "easily tearable film and pouch made therefrom". The film has an easily tearable thin walled part incorporating two strings into the plastic film, both of which are generally adjacent one edge of the pouch. Notches are provided between the two strings.
See, also, U.S. Pat. Nos. 2,307,735; 3,323,707; 3,494,538; 3,759,439; 4,720,366; 4,834,245; 4,883,625; 4,769,202; 4,903,841; 4,903,843; and 5,139,593; Japanese Patent Publication Nos. 123256/1981; 26450/1984 and 13661/1985; German Patent Publication No. DE 41 09 605; Netherlands Patent Publication No. NL 8600546; Swiss Patentschrift No. 384,452; and PCT International Patent Publication No. 92/16431.